Flexographic printing is a rotary letter press printing process which traditionally uses flexible rubber, or other elastomer, printing plates and liquid, fast drying ink. The advantage of flexographic printing is its simple ink distribution system.
Referring to FIGS. 1 and 2, in a flexographic printing device 110, a web 100 to be imprinted is passed between an impression cylinder 112 and a plate or print cylinder 114 from which the ink is transferred to the web 100. Ink is applied to the plate cylinder 114 in precisely controlled quantities by a transfer or anilox metering roll 116. The circumferential surface of the anilox roll 116 is divided into a very large number of small cells (typically, 15,000 cells per square centimeter). The surface of the anilox roll 116 is flooded with ink, filling the cells on the roll's surface. Ink is fed to the anilox roll 116 by an ink fountain 118. Typically, the ink fountain 118 extends the entire length of the anilox roll 116 and plate cylinder 114.
A commonly-used ink fountain comprises a reverse angle doctor blade 122b which meters the surface of the anilox roll 116 and a second doctor blade 122a which forms a sealed ink chamber 120 between the two blades. This system uses the surface tension of the ink itself to load the ink onto the anilox roll 116 so the chamber 120 does not have to be pressurized. Typically, ink is pumped into the base of the chamber 120 through a pair of lower inlets 126. As the ink is pumped into the chamber, the level of the ink within the chamber rises to the level of the overflow outlets 128 where it drains back to the ink supply. Ink flow is maintained by a pump, gravity-return system.
As the anilox roll 116 rotates, the doctor blades 122a and 122b shave surplus ink from the surface of the anilox roll 116 so that ink is carried only in the interior of the cells of the roll surface and not on the lands between cells. This results in a uniformly-metered film of ink being applied to the surface of the plate cylinder 114.
Standing waves and areas of sluggish flow are common in these conventional chambered doctor blade systems which have only one or two non-angled inlet supply ports and results in less rewetability and chemical uniformity of the ink supplied to the anilox roll.
In addition, the wash-up of the deck (the fountain 118 and anilox roll 116) of conventional chambered doctor blade flexographic presses has been time-consuming and costly. Wash-up is considered to be the biggest part of a job changeover. Whenever the ink is changed in the press (for color, consistency, etc.), the old ink must be removed. In the past, it has been necessary to employ a separate high pressure water source for spray cleaning the anilox roll. Such a cleaning method has the potential to damage the surface of high cell per inch rolls.
The present invention ensures uniform ink circulation throughout the chamber and greatly improves wash-up efficiency by eliminating the need for a separate high pressure water source for spray cleaning the anilox roll.